the system size is then limited to IP Addressing only). The maximum number of networks connected in series to the local network via Network Bridges is seven (i.e. using six network bridges). Each standard C-Bus unit requires 18mA @ 15-36Vdc to operate, however some C-Bus units require up to 40mA. More than one C-Bus power supply can be connected to a C-Bus network to provide sufficient power to the C-Bus units, the C-Bus power supplies will share the load evenly. Each C-Bus network requires a network burden if there are insufficient C-Bus units on the network. This network burden can be enabled on C-Bus output units through software or a hardware burden can be connected to the network. Each C-Bus network requires at least one system clock generating unit for data synchronisation. The isolation between the mains supply circuitry and the 36 V DC C-Bus circuitry is greater than 3.5 kV. This is achieved using double wound transformers and opto isolators. This means the C-Bus wiring, connections and circuitry can be considered Extra Low Voltage. Wiring Design of C-Bus Systems With conventional wiring, the mains power (120 / 230 V) is wired from the distribution board (DB) to the load (for example, a ceiling light) via a wall switch. In C-Bus systems, the connections between the DB and (for example) the ceiling lights, and between the DB and the junction box (wall switch) are completely separate. In addition, there are no connections between the junction box and the respective ceiling lights. The power control in a C-Bus system lies in a “Dimmer” or “Relay” which is installed in the DB and replaces the traditional switch used in conventional wiring. This Dimmer (or Relay) has a 120/230 V Line interconnection directly to the ceiling light and a neutral connection back from the ceiling light to the Dimmer. The Dimmer will control the light directly and will receive its commands from another device on the C-Bus network (for example, a wall mounted light switch/keypad). This wall mounted light switch would not be connected to any load whatsoever; it would be directly connected with the Dimmer by means of a control/signalling cable. The Dimmers normally come as 4-, 8- or 12-channel DIN-rail mounted devices. C-Bus Interoperability As of 9 December 2008 Clipsal opened its C-Bus protocols to anyone who wants to interact with it programatically. Using one of Clipsal's C-Bus interface modules (PCI